Closed type waterborne polyurethane plant protein composite adhesive and preparation method thereof

Abstract

The present application relates to the technical field of adhesive, in particular to a kind of closed water-based polyurethane plant protein composite adhesive and preparation method thereof.The present application includes the following steps: step one, castor oil, isophorone diisocyanate is mixed uniformly, then heated to obtain the first mixture;Step two, 2,2-dimethylol propionic acid, triethylamine are added to the first mixture to obtain the second mixture, step three, imidazole is added to the second mixture to obtain the third mixture, the third mixture is emulsified by adding the second deionized water to obtain the closed water-based polyurethane;Deionized water is added to protein powder, stirred uniformly to obtain protein powder slurry, the pH of protein powder slurry is adjusted using sodium hydroxide, then the closed water-based polyurethane is added dropwise into the protein powder slurry to obtain the closed water-based polyurethane plant protein composite adhesive, and the method can prepare the closed water-based polyurethane plant protein composite adhesive with suitable deblocking temperature and good bonding performance.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to a closed waterborne polyurethane plant protein composite adhesive and a preparation method thereof. Background Art

[0002] Polyurethane adhesives are made from polymer materials. The primary repeating units in their molecular chains are urethane (-NHCOO-) or isocyanate (-NCO). Because polyurethanes are hard- and soft-block compounds, they possess both rigidity and flexibility. Their diverse molecular structures contribute to their diverse properties, leading to their widespread application.

[0003] Waterborne polyurethanes are polyurethane products that use water as a solvent or dispersion. Because they contain no or only a small amount of organic solvents, they are more environmentally friendly than solvent-based polyurethanes, with low VOC emissions, no pollution, and are non-flammable. Consequently, they are widely used in a variety of fields, including packaging, construction, electronic components, and printing.

[0004] Waterborne polyurethane adhesives include blocked waterborne polyurethane adhesives. During the preparation process, a blocked waterborne polyurethane adhesive is first reacted to produce an isocyanate-terminated polyurethane prepolymer containing urethane structural units. This is then reacted with a blocking agent to produce a blocked polyurethane prepolymer. Finally, the prepolymer is neutralized with a neutralizing agent and emulsified with water to produce a fully water-based blocked polyurethane adhesive. During use, the blocked waterborne polyurethane adhesive is heated to a certain temperature to release the NCO groups. The active NCO groups then cross-link with the active hydrogen of the substrate to form chemical bonds, achieving the adhesive's bonding strength and water resistance.

[0005] Soy protein polyurethane has good adhesive properties, wide use and sustainable advantages. Due to its environmental protection and sustainability characteristics, it is becoming an important research direction in the adhesive field.

[0006] Among them, the current preparation method of soybean protein polyurethane composite adhesive is:

[0007] Dehydrated polyethylene glycol, isophorone diisocyanate, and the catalyst dibutyltin dilaurate are first reacted to form a mixture. Then, dimethyl butynedioate, dimethyl oxalate, and butadiene are added dropwise as chain extenders until the isocyanate groups in the polymer are completely reacted, producing a CWPOU crosslinker emulsion. This crosslinker emulsion is then mixed with soy protein powder, followed by the addition of 1,2,3-propylene glycol diglycidyl ether as a curing agent to produce the soy protein polyurethane.

[0008] The above-mentioned preparation method of soy protein polyurethane composite adhesive still has shortcomings:

[0009] It requires the use of catalysts and toxic reagents such as chain extenders DMAD, DMO and BD to extend the chain to obtain a cross-linker, and then use a curing agent (PTGE) to connect the cross-linker with soy protein. The synthesis process is complicated and not environmentally friendly. Summary of the Invention

[0010] The purpose of the present invention is to avoid the shortcomings of the prior art and provide a method for preparing a closed water-based polyurethane plant protein composite adhesive. The method for preparing a closed water-based polyurethane plant protein composite adhesive can produce a closed water-based polyurethane plant protein composite adhesive with a suitable unblocking temperature and good bonding performance in an environmentally friendly and low-cost manner.

[0011] To achieve the above objectives, the present invention provides the following technical solutions:

[0012] Provided is a method for preparing a closed waterborne polyurethane plant protein composite adhesive, comprising the following steps:

[0013] Step 1: Mix castor oil and isophorone diisocyanate uniformly, then heat to 60-80° C., and stir for 1.5-3 hours to obtain a first mixture;

[0014] Step 2: adding 2,2-dihydroxymethylpropionic acid and triethylamine to the first mixture to obtain a transparent and viscous second mixture;

[0015] Step 3: adding imidazole to the transparent and viscous second mixture and stirring the mixture at 50° C. to 70° C. for 1.5 to 3 hours to obtain a third mixture; adding deionized water to the third mixture for emulsification to obtain a blocked waterborne polyurethane;

[0016] Step 4: Use protein powder, add deionized water to the protein powder, stir evenly to obtain protein slurry, use sodium hydroxide solution to adjust the pH of the protein slurry to 9-10, and then add the blocked water-based polyurethane dropwise to the protein powder slurry, wherein the amount of the blocked water-based polyurethane added is 10% to 70% of the amount of the protein slurry, stir evenly, and obtain a plant protein composite adhesive.

[0017] In some embodiments, in step 3, the weight ratio of the second mixture to the imidazole is 15 to 30:1.

[0018] In some embodiments, the protein powder is waste plant protein.

[0019] In some embodiments, the plant is soybean or cottonseed bean.

[0020] In some embodiments, in step 1, the heating environment is a nitrogen atmosphere.

[0021] The beneficial effects of the preparation method of the closed waterborne polyurethane plant protein composite adhesive of the present invention are as follows:

[0022] (1) The present invention provides a method for preparing a closed water-based polyurethane plant protein composite adhesive, which fully utilizes the protein structure and the water-based polyurethane structure to prepare an environmentally friendly closed water-based polyurethane plant protein composite adhesive. Specifically, water-based polyurethane is first prepared, and the water-based polyurethane is combined with the protein molecules through physical bonding, which effectively strengthens the multiple structures of the protein and improves the cross-linking tightness. The long-chain fatty acid structure of the cross-linking system serves as a soft segment, providing the adhesive with good wettability and flexibility, thereby avoiding the problem of insufficient bonding performance caused by rigid structural defects in traditional cross-linking modification systems, which in turn affects the bonding performance. In addition, the protein structure is unfolded by alkali solution to expose the reactive groups. When water-based polyurethane is introduced into the protein system, the water-based polyurethane can better bind to the protein, inducing the system to produce a microphase separation structure, and providing bonding strength through the covalent bond cross-linking network. The above-mentioned water-based polyurethane and protein molecules jointly assist the protein glue system in dissipating energy when under stress through the physical hydrogen bond cross-linking network and microphase separation structure, effectively improving the toughness of the adhesive, jointly ensuring the structural integrity of the adhesive, and effectively improving the cohesive strength and water and heat resistance of the adhesive, with even better performance.

[0023] (2) The preparation method of a closed water-based polyurethane plant protein composite adhesive of the present invention contains protein and water-based polyurethane structure. When the closed water-based polyurethane plant protein composite adhesive is heated, the active groups can be unblocked, so that they can react with proteins. Under the multiple bonding effects of chemical bonds and hydrogen bonds, a cross-linked network is formed, which enhances the surface hydrophobicity of the adhesive and improves the wet bonding strength of the protein adhesive.

[0024] (3) The preparation method of a closed waterborne polyurethane protein composite adhesive of the present invention does not require the use of complex process toxic reagents such as catalyst DBTDL, chain extender DMAD, DMO and BD to synthesize the crosslinker, and does not require the use of a curing agent to combine the crosslinker and protein. It has the advantages of being environmentally friendly, low cost and easy to operate.

[0025] (4) The preparation method of a closed water-based polyurethane plant protein composite adhesive of the present invention does not use organic reagents as solvents or toxic or harmful catalysts. The main raw materials are derived from waste biomass. By adding an appropriate amount of protein modifier and water-based polyurethane, heating and stirring at a certain temperature, the operation is simple. The addition of NaOH as a modifier strengthens the effective cross-linking between protein and protein, and between polyurethane and protein, without the need to prepare an additional cross-linking agent, thereby improving the cross-linking tightness. The prepared protein-based adhesive is green, formaldehyde-free, and low in cost. It has a simple structure, uses less materials, and is suitable for large-scale production and application.

[0026] Also provided is a closed waterborne polyurethane plant protein composite adhesive, which is prepared by the above-mentioned preparation method of the closed waterborne polyurethane plant protein composite adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the infrared spectrum test chart of Test Example 1.

[0028] Figure 2 This is the infrared spectrum test chart of Experimental Example 2.

[0029] Figure 3 This is the XPS test chart of Experimental Example 3.

[0030] Figure 4 This is the adhesive strength test of Test Example 4. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0032] Example

[0033] The preparation method of the closed waterborne polyurethane plant protein composite adhesive disclosed in this embodiment comprises the following steps:

[0034] Step 1: uniformly mix castor oil and isophorone diisocyanate, then heat to 60-80° C., preferably 70° C., under a nitrogen environment, and stir for 1.5-3 hours, preferably 2 hours, to obtain a first mixture;

[0035] Step 2: adding 2,2-dimethylolpropionic acid and triethylamine to the first mixture to obtain a transparent and viscous second mixture, and adding first deionized water for emulsification. The amount of the first deionized water can be selected according to the actual situation to obtain a waterborne polyurethane;

[0036] Step 3: adding imidazole to the transparent and viscous second mixture and stirring at 50° C. to 70° C. for 1.5 to 3 hours to obtain a third mixture; adding 80 g of the second deionized water to the third mixture for emulsification to obtain a blocked waterborne polyurethane;

[0037] Step 4: Use protein powder, add deionized water to the protein powder, stir evenly to obtain protein slurry, use sodium hydroxide solution to adjust the pH of the protein slurry to 9-10, preferably pH 9, then add the water-based polyurethane dropwise to the protein powder slurry, the addition amount of the blocked water-based polyurethane is 10% to 70% of the amount of the protein slurry, stir evenly, and obtain a plant protein composite adhesive.

[0038] In this embodiment, in step 2, the weight ratio of the castor oil, the isophorone diisocyanate, the 4-dimethylaminopyridine, and the triethylamine is 8-10:3-7:1-2:1.5-3, preferably 9.3:6.7:1.3:1.1, and the weight of the raw materials can be adjusted according to actual needs.

[0039] In this embodiment, in step 3, the weight ratio of the second mixture to the imidazole is 19:1, and the weight of the raw materials can be adjusted according to actual needs.

[0040] In this embodiment, the protein powder is waste plant protein, preferably soybean or cottonseed meal. The specific type of protein powder can be selected according to actual needs.

[0041] Performance test

[0042] To illustrate the performance of the blocked waterborne polyurethane plant protein composite adhesive prepared by the present invention, the following experimental performance tests were performed:

[0043] Each abbreviation represents the following, respectively:

[0044] CPC purified cottonseed protein powder slurry

[0045] BWPU blocked waterborne polyurethane

[0046] WPU waterborne polyurethane

[0047] CPC / BWPU closed waterborne polyurethane protein composite adhesive

[0048] CPC / WPU water-based polyurethane protein composite adhesive

[0049] Test Example 1

[0050] Sample preparation:

[0051] Step 1: 9.32 g of castor oil and 6.66 g of isophorone diisocyanate were mixed uniformly, and then heated to 70° C. under nitrogen environment with stirring for 2 h to obtain a first mixture;

[0052] Step 2: Add 1.38 g of 2,2-dimethylolpropionic acid and 1.1 g of triethylamine to the first mixture to obtain a transparent and viscous second mixture, wherein deionized water is added to emulsify the mixture to obtain a waterborne polyurethane WPU, which is subsequently used for comparative testing;

[0053] Step 3: Add 1.1 g of imidazole to the transparent and viscous second mixture, stir and react at 60° C. for 2 h to obtain a third mixture, and add 80 g of the second deionized water to the third mixture for emulsification to obtain a blocked waterborne polyurethane BWPU;

[0054] The obtained WPU and BWPU were subjected to the following tests:

[0055] The test results are as follows Figure 1 As shown, the infrared spectrum of BWPU ( Figure 1 a) Medium, 3320~3620cm -1 The broad absorption peak at 2933 cm corresponds to the -NH stretching vibration peak of carbamate and allophanate. -1 The stretching vibration peak of methyl group is at 2857cm -1 The peak at 1710cm is the bending vibration peak of methylene. -1 The peak can be attributed to the stretching vibration absorption peak of -C=O of carbamate. Before the end capping, part of the -NCO reacts with the -OH in DMPA to form a carbamate bond. After the end capping, part of the -NCO continues to react with imidazole to form a carbamate carbonyl and a urea carbonyl. Therefore, the peak at 1710 cm is generated after the end capping. -1 and 1640cm -1 There is a sharp strong absorption peak at Figure 1 It can be clearly seen that before closing 2275cm -1 There is an obvious absorption peak at 2840~2930cm -1 The peak at 47° was enhanced, indicating that there was no -NCO group in the system after blocking, and the imidazole-terminated water-based polyurethane emulsion was successfully prepared.

[0056] When the BWPU sample was placed in a 130℃ temperature environment for 400s, its infrared spectrum ( Figure 1 b) at 2270 cm -1 The characteristic absorption peak attributed to isocyanate appears at 1530 cm -1The intensity of the characteristic absorption peak attributed to -NH bending vibration decreases, indicating that the blocking and unblocking of isocyanate are achieved. The unblocking temperature of BWPU is characterized by DSC test. The type of blocking agent and isocyanate affects the unblocking temperature of blocked waterborne polyurethane. The unblocking temperature of imidazole blocking agent is generally between 110 and 130 °C. Figure 1 In the DSC test of c, the BWPU curve shows an obvious deblocking endothermic peak, and the starting position of the endothermic peak is at 100℃, indicating that the blocker begins to deblock at this temperature; when the temperature rises to 105℃, the deblocking reaction endothermic peak reaches its maximum value, indicating that the deblocking reaction is fastest at this time; then the endothermic peak gradually decreases until there is no endothermic peak at 115℃, indicating that the deblocking reaction has been completed. The wider curve range in the DSC graph shows that the deblocking reaction of imidazole and isocyanate is a process in which the active -NCO is gradually released as the temperature rises, and Figure 1 Figure d shows the unblocking process of blocked waterborne polyurethane under hot pressing. The maximum unblocking temperature is 115°C, which is suitable to meet the hot pressing temperature during the use of the adhesive. It overcomes the problem that the unblocking temperature of traditional blocking agents is too high, making it difficult to unblock and bond, or the unblocking temperature is too low, causing bonding during transportation.

[0057] Test Example 2

[0058] To further illustrate the relationship between CPC, WPU, BWPU, CPC / WPU, and CPC / BWPU, the following tests were performed:

[0059] Sample preparation:

[0060] Step 1: 9.32 g of castor oil and 6.66 g of isophorone diisocyanate were mixed uniformly, and then heated to 70° C. under nitrogen environment with stirring for 2 h to obtain a first mixture;

[0061] Step 2: Add 1.38 g of 2,2-dihydroxymethylpropionic acid and 1.1 g of triethylamine to the first mixture to obtain a transparent and viscous second mixture, wherein the first deionized water is added for emulsification to obtain a waterborne polyurethane WPU, which is used for subsequent comparative tests.

[0062] Step 3: Add 1.1 g of imidazole to the transparent and viscous second mixture, stir and react at 60° C. for 2 h to obtain a third mixture, and add 80 g of the second deionized water to the third mixture for emulsification to obtain a blocked waterborne polyurethane BWPU;

[0063] Step four, using protein powder, adding deionized water to the protein powder, stirring evenly to obtain a protein slurry, using sodium hydroxide solution to adjust the pH of the protein slurry to 9, then adding the blocked waterborne polyurethane to the protein slurry, the amount of blocked waterborne polyurethane added is 50% of the amount of protein slurry, stirring evenly to obtain a plant protein composite adhesive sample CPC / BWPU.

[0064] To further illustrate the comparison effect, a protein powder is also used, deionized water is added to the protein powder, stirring evenly to obtain a protein slurry, sodium hydroxide solution is used to adjust the pH of the protein slurry to 9, then the waterborne polyurethane WPU is added to the protein slurry, the amount of waterborne polyurethane added is 50% of the amount of protein slurry, stirring evenly to obtain a non-blocked plant protein composite adhesive sample CPC / WPU.

[0065] The FTIR spectra of CPC, WPU, BWPU, CPC / WPU, CPC / BWPU adhesives are shown in Figure 2 The FTIR spectrum of WPU shows a -N-H stretching vibration peak at 3310 cm -1 , a -C=O stretching vibration peak at 1723 cm -1 , and a -N-H bending vibration peak at 1532 cm -1 . In CPC, the associated peaks of -O-H and -N-H stretching vibrations in proteins are at 3000-3500 cm -1 , the symmetric and asymmetric stretching vibrations of C-H are at 2800-3000 cm -1 , and the characteristic peaks of the stretching vibrations of C-N in amide III region are at 1637 cm -1 , 1543 cm -1 , and 1215 cm -1 , respectively. These characteristic absorption peaks form red shift or blue shift under the influence of multiple hydrogen bonds. Under heat pressing, the blocked isocyanate groups in BWPU are unblocked and react with the polar groups such as amino or hydroxyl groups in proteins to further form a chemical crosslinking network. However, the generated urethane or urea groups are masked by the amide bonds in proteins, and the characteristic peak of -NCO at 2270 cm -1 is not found in the figure. Therefore, we further prove by experiment example 3 that the isocyanate groups are unblocked and form a chemical crosslinking network with proteins.

[0066] Test Example 3

[0067] In order to further verify the interaction mechanism between BWPU and plant protein powder, XPS was used to study the composition of chemical bonds in BWPU in Experimental Example 1. Figure 3 As shown in the figure, from the spectrum of C1s peak fitting of the protein composite adhesive, it can be obtained that the characteristic peaks at 284.7eV, 286.4eV, and 288.2eV are attributed to C1 (-CC / -CH), C2 (-CO / -CN), and C3 (-C=O), respectively. After adding BWPU, it was found that the proportion of C2 in the CPC / BWPU composite adhesive increased from 9.09% to 12.29%, and the proportion of C3 increased from 12.29% to 14.64%. The reason for the increase in the proportion of C2 and C3 is that the isocyanate groups deblocked by BWPU react with the amino and hydroxyl groups in the protein to form carbamate or urea groups. The N1S peak fitting spectrum of the protein composite adhesive provides key evidence that thermally excited isocyanate groups consume amino groups to form a chemical cross-linking network. The figure shows that the two characteristic peaks in the N1s region at 399.8eV and 401.1eV are attributed to N1 (-R-NH-) and N2 (R-NH2). The proportion of N2 is related to the number of free amino groups in the adhesive. When BWPU is added, the proportion of N2 decreases from 9.61% to 5.73%, confirming that BWPU, under thermal excitation, does release isocyanate groups and consume amino groups.

[0068] Test Example 4

[0069] Sample preparation:

[0070] Step 1: 9.32 g of castor oil and 6.66 g of isophorone diisocyanate were mixed uniformly, and then heated to 70° C. under nitrogen environment with stirring for 2 h to obtain a first mixture;

[0071] Step 2: Add 1.38 g of 2,2-dihydroxymethylpropionic acid and 1.1 g of triethylamine to the first mixture to obtain a transparent and viscous second mixture, wherein the first deionized water is added for emulsification to obtain a waterborne polyurethane WPU, which is used for subsequent comparative tests.

[0072] Step 3: Add 1.1 g of imidazole to the transparent and viscous second mixture, stir and react at 60° C. for 2 h to obtain a third mixture, and add 80 g of the second deionized water to the third mixture for emulsification to obtain a blocked waterborne polyurethane BWPU;

[0073] Step 4: Use protein powder, add deionized water to the protein powder, stir evenly to obtain protein slurry, use sodium hydroxide solution to adjust the pH of the protein slurry to 9, and then add the blocked waterborne polyurethane dropwise to the protein slurry. The amount of blocked waterborne polyurethane added is 50% of the amount of protein slurry. Stir evenly to obtain a plant protein composite adhesive sample CPC / BWPU.

[0074] To further illustrate the comparative effect, protein powder was also used, deionized water was added to the protein powder, and the mixture was stirred evenly to obtain a protein slurry. The pH of the protein slurry was adjusted to 9 using a sodium hydroxide solution, and then the water-based polyurethane WPU was added dropwise to the protein slurry. The amount of water-based polyurethane added was 10%, 30%, 50%, and 70% of the amount of the protein slurry. The mixture was stirred evenly to obtain a non-enclosed plant protein composite adhesive sample CPC / WPU.

[0075] The test results are as follows Figure 4 As shown in the dry adhesive strength test, when the WPU addition level was 0%, the dry adhesive strength of the adhesive was 1.78 MPa. As the WPU addition level increased from 0 to 50%, the dry adhesive strength gradually increased. At addition levels of 10% and 30%, the dry adhesive strengths were 1.97 MPa and 2.42 MPa, respectively; at a 50% addition, the dry adhesive strength reached 2.65 MPa. In the wet adhesive strength test, the wet adhesive strength remained around 0.9 MPa for WPU additions of 0% to 10%. Further increasing the WPU addition level significantly increased the wet adhesive strength, reaching 1.23 MPa at a 50% WPU addition. When WPU was replaced with BWPU, both the dry and wet adhesive strengths of the CPC / BWPU adhesive were further improved, indicating that the CPC / BWPU adhesive possesses even better adhesive strength. The bonding strength of the adhesive prepared in this experiment is much higher than the requirements for Class II plywood in GB / 17657-2013 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels".

[0076] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a closed waterborne polyurethane plant protein composite adhesive, characterized in that: The following steps are involved: Step 1: Mix castor oil and isophorone diisocyanate uniformly, then heat to 60° C. to 80° C., and stir for 1.5 h to 3 h to obtain a first mixture; Step 2: adding 2,2-dihydroxymethylpropionic acid and triethylamine to the first mixture to obtain a transparent and viscous second mixture; Step 3: adding imidazole to the transparent and viscous second mixture and stirring the mixture at 50° C. to 70° C. for 1.5 to 3 hours to obtain a third mixture; adding deionized water to the third mixture for emulsification to obtain a blocked waterborne polyurethane; Step 4: Use protein powder, add deionized water to the protein powder, stir evenly to obtain protein slurry, use sodium hydroxide solution to adjust the pH of the protein slurry to 9-10, and then add the blocked water-based polyurethane dropwise to the protein powder slurry, wherein the amount of the blocked water-based polyurethane added is 10% to 70% of the amount of the protein slurry, stir evenly, and obtain a plant protein composite adhesive.

2. The method for preparing a closed waterborne polyurethane plant protein composite adhesive according to claim 1, wherein: In step 3, the weight ratio of the second mixture to the imidazole is 15 to 30:

1.

3. The method for preparing a closed waterborne polyurethane plant protein composite adhesive according to claim 1, wherein: The protein powder is waste plant protein.

4. The method for preparing a closed waterborne polyurethane plant protein composite adhesive according to claim 1, wherein: The plants are soybean and cottonseed meal.

5. The method for preparing a closed waterborne polyurethane plant protein composite adhesive according to claim 1, wherein: In step 1, the heating environment is a nitrogen atmosphere environment.

6. A closed waterborne polyurethane plant protein composite adhesive, characterized in that: The adhesive is prepared by the method for preparing the closed waterborne polyurethane plant protein composite adhesive according to any one of claims 1 to 5.

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